We have designed a genetic screen to identify human genes that alter iron homeostasis when expressed in yeast. Human genes for the iron-storage protein ferritin have been expressed in yeast, and although the proteins are stable and assemble into the proper 24-subunit oligomer, only a small amount of iron is deposited within the ferritin core. We hypothesize that cytosolic iron chaperones that facilitate iron loading into ferritin may be expressed in human cells, but not in yeast, which do not synthesize ferritin. We have isolated multiple human cDNAs which, when expressed in a yeast cell that contains human ferritin, increase the transfer of cytosolic iron into ferritin. Using siRNA in cultured human cell lines, we have also determined that depletion of poly-C binding protein 1 (PCBP1) results in a defect in ferritin iron loading. Co-immunoprecipitation experiments indicate that PCBP1 binds to ferritin in vivo, but only in the presence of reduced iron. PCBP1 binds ferrous iron in vitro with micromolar affinity and can donate iron to ferritin in vitro. We propose that PCBP1 can function in yeast and human cells as an iron chaperone, and enhance the loading of iron into ferritin.